MAXI/GSC detection of X-ray activity from X-ray pulsar XTE J1829-098

ATel #11927; M. Nakajima, H. Negoro (Nihon U.), S. Nakahira (RIKEN), A. Sakamaki, W. Maruyama (Nihon U.), T. Mihara, F. Yatabe, Y. Takao, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, Y. Kawakubo, T. Hashimoto, A. Yoshida (AGU), N. Kawai, M. Sugizaki, Y. Tachibana, K. Morita (Tokyo Tech), S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara, N. Isobe, R. Shimomukai (JAXA), Y. Ueda, A. Tanimoto, T. Morita, S. Yamada (Kyoto U.), Y. Tsuboi, W. Iwakiri, R. Sasaki, H. Kawai, T. Sato (Chuo U.), H. Tsunemi, T. Yoneyama (Osaka U.), M. Yamauchi, K. Hidaka, S. Iwahori (Miyazaki U.), T. Kawamuro (NAOJ), K. Yamaoka (Nagoya U.), M. Shidatsu (Ehime U.)
on 9 Aug 2018; 21:38 UT
Credential Certification: Motoki Nakajima (nakajima.motoki@nihon-u.ac.jp)

Tweet

The MAXI/GSC nova-alert system (Negoro et al. 2016, PASJ, 68, S1) detected a weak X-ray flux enhancement from the Galactic plane (l,b) = (22.0, 0.0) on 2018-08-06T17:04(UT). Assuming that the source flux was constant over 8 times scan transit (2018-08-07T05:26(UT) to 16:15), we have obtained the source position at (R.A., Dec) = (277.752 deg, -9.630 deg) = (18 31 00, -09 37 48) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.34 deg and 0.31 deg, respectively. The roll angle of long axis from the north direction is 172.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). This position nicely matched with the 7.8 second transient X-ray pulsar XTE J1829-098 ((RA,DEC)=(277.43,-9.86)) (Markwardt et al. 2004, Atel#317). This is the first detection of XTE J1829-098 by MAXI/GSC since August 2009.

The MAXI/GSC data shows that the present brightening started from 2018-08-05 (MJD 58335). The daily averaged 4-10 keV flux reached 0.028 +- 0.005 photons/s/cm² (24 +- 4 mCrab) on 2018-08-07 (MJD 58337), and slightly decreased to 0.021 +- 0.005 photons/s/cm² (18 +- 4 mCrab) on 2018-08-08 (MJD 58338). This X-ray flux variation traces the previous outburst profile, a duration of ∼7 days (Markwardt et al. 2009, Atel#2007). The 2-10 keV X-ray spectrum integrated over 4 days (MJD 58335-58338) can be described by unabsorbed power-law model with photon index of 0.31^+0.48_-0.52 (90% C.L.), which is consistent with the previous report of Γ = 0.76 +- 0.13 (Halpern et al. 2007, ApJ, 669, 579). The observed luminosity in 2-10 keV energy band is 3.6×10³⁶ (d/10 kpc)² erg s^-1, which is larger than the previous outburst peak luminosity by a factor of ∼4.

Previously, two outburst periodicities were claimed by Halpern et al. 2007 (∼1.3yr) and Markwardt et al. 2009 (∼246d). The multiple of the above two periods do not match with the time interval between the current brightening and the last outburst in 2009. However if small modifications (a few days) are applied on both periodicities, the time interval becomes multiple of its. Moreover, the time interval is 14 times the modified Markwardt's prediction of ∼243d (or half of the Halpern's period). Therefore, we can not rule out each periodicity.